Many scientific publications strongly suggest that regular consumption of significant amounts of polyunsaturated fatty acids can deliver important health benefits. In recent years, ω-3 polyunsaturated fatty acids, especially the ω-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have become more important.
DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end. Its trivial name is cervonic acid, its systematic name is (4Z,7Z,10Z,13Z,16Z,19Z)-docosa-4,7,10,13,16,19-hexaenoic acid, and its shorthand name is 22:6(n-3) in the nomenclature of fatty acids.
Cold-water oceanic fish oils are rich in DHA. Most of the DHA in fish and complex organisms with access to cold-water oceanic foods originates in photosynthetic and heterotrophic microalgae, and becomes increasingly concentrated in organisms, as they move up the food chain. DHA is also commercially manufactured from microalgae, such as Crypthecodinium cohnii. Some animals with access to seafood make very little DHA through metabolism, but obtain it in the diet. However, in strict herbivores, and carnivores that do not eat seafood, DHA is manufactured internally from α-linolenic acid, a shorter omega-3 fatty acid manufactured by plants (and also occurring in animal products as obtained from plants).
DHA is metabolized to form the docosanoids, which comprise several families of potent hormones. DHA is a major fatty acid in sperm and brain phospholipids, particularly in the retina. Dietary DHA may reduce the risk of heart disease by reducing the level of blood triglycerides in humans.
EPA is a carboxylic acid with a 20-carbon chain and five cis double bonds; the first double bond is located at the third carbon from the omega end. Its trivial name is timnodonic acid, its systematic name is (5Z,8Z,11Z,14Z,17Z)-eicosa-5,8,11,14,17-pentenoic acid, and its shorthand name is 20:5(n-3) in the nomenclature of fatty acids.
EPA and its metabolites act in the body largely by their interactions with the metabolites of arachidonic acid. EPA acts as a precursor for prostaglandin-3 (which inhibits platelet aggregation), thromboxane-3, and leukotriene-5 groups (all eicosanoids).
Like DHA, EPA is obtained in the human diet by eating oily fish or fish oil, e.g., cod liver, herring, mackerel, salmon, menhaden and sardine. It is also found in human breast milk. Fish do not naturally produce EPA, but obtain it, as with DHA, from the algae they consume.
The human body can convert α-linolenic acid to EPA, but this is much less efficient than resorption of EPA from food containing it. Because EPA is also a precursor to DHA, ensuring a sufficient level of EPA in a diet containing neither EPA nor DHA is harder both because of the extra metabolic work required to synthesize EPA and because of the use of EPA to metabolize DHA. Medical conditions like diabetes or certain allergies may significantly limit the human body's capacity for metabolization of EPA from α-linolenic acid.
The US National Institute of Health's MedlinePlus lists medical conditions for which EPA (alone or in concert with other ω-3 sources) is known or thought to be an effective treatment. Most of these involve its ability to lower inflammation.
Among omega-3 fatty acids, in particular EPA is thought to possess beneficial potential in mental conditions, such as schizophrenia. Several studies report an additional reduction in scores on symptom scales used to assess the severity of symptoms, when additional EPA is taken.
Many efforts have been made by the industry to develop food products and nutritional preparations that contain appreciable amounts of EPA and/or DHA. However, edible products containing appreciable levels of EPA and/or DHA tend to develop an off-flavour during storage. This off-flavour problem is associated with the oxidation of EPA and DHA. Oxidation of these particular polyunsaturated fatty acids is accompanied by the formation of volatile, potent flavour molecules, such as unsaturated aldehydes. Flavour attributes associated with the oxidation products of EPA and DHA include “cardboard”, “paint”, “oily”, “rancid”, “grass”, “metallic” and “fish”. These off-flavour notes are particularly objectionable in food products such as spreads.
It is generally assumed that food products should contain relatively high levels of EPA and DHA to have the desired beneficial health effects like reduced platelet aggregation and reduced blood triglycerides. However, efforts in the industry to employ high levels EPA and DHA in food products have been frustrated by the tendency of these products to quickly develop an off-flavour during storage.
Water-and-oil emulsions containing appreciable levels of EPA and DHA are particularly sensitive to off-flavour development, presumably because oxygen contained in the water phase can react with the EPA and DHA at the oil-water interface and/or because the oxidation of EPA and DHA is catalyzed by components contained in the aqueous phase, such as traces of copper or iron. In water-in-oil emulsions such as spreads, off-flavour formation as a result of oxidation of EPA and DHA is a particularly challenging problem as spreads have a rather bland taste and are usually consumed over a period of weeks during which time the product is in direct contact with atmospheric oxygen.
EP-A 1 180 545 describes plant sterol-containing fat compositions comprising a plant sterol fatty acid ester and a partial glyceride. The Examples describe the preparation of a margarine comprising 54 wt. % of an aqueous phase, 27.6% by weight of a hardened fish oil (melting point: 36° C.) and 18.4% by weight of a plant sterol containing composition (containing 49 wt. % plant sterol fatty acid ester).
US 2007/0054028 relates to the use of non-esterified phytosterols in formulating fat-containing dietary supplements and direct food additives, and in fortifying prepared foods. It is observed in the US patent application that non-esterified phytosterols were found to have the property of decreasing the oxidation of fats used in these supplements and prepared foods, particularly the oxidation of triglycerides containing polyunsaturated fatty acids including linoleic and alpha-linolenic acid and also the more perishable fatty acids found in fish oil, e.g. DHA and EPA.
WO 2009/068651 describes oil-in-water emulsions suitable for direct human consumption, comprising a triglyceride oil having a solid fat content in the range of ambient to body temperature, galactolipid, and a sterol of vegetable origin selected from a phytosterol, a phytostanol, an ester of a phytosterol, an ester of a phytostanol and their mixtures.
Micallef et al. (“Beyond blood lipids: phytosterols, statins and omega-3 polyunsaturated fatty acid therapy for hyperlipidemia”, Journal of Nutritional Biochemistry 20 (2009, 927-939) observe that phytosterols and omega-3 fatty acids are natural compounds with potential cardiovascular benefits. The authors conclude that it would be desirable to develop a single functional food incorporating phytosterols and omega-3 fatty acids for ease of consumption and improved compliance.